The present invention relates to a vacuum cleaner and, more particularly, to method and an apparatus for operating a vacuum cleaner in an optimum condition in accordance with the state of the cleaning surface and the choking state of the cleaner.
In vacuum cleaners, the suction is set to a constant value irrespective of the state of the cleaning surface. Therefore, the suction force is either too strong or too weak for the cleaning surface or an object to be cleaned, so that the optimum control which is comfortable to the user cannot be performed.
To solve this problem, such an optimum control can be realized by, for example, controlling the motor of the cleaner to adjust the suction in accordance with the cleaning surface. As a method of adjusting the suction force of the cleaner, a method whereby the rotational speed of the drive motor is variably set is first considered. As ways of changing the rotational speed of the motor, there have been known a method in which the phase is controlled using a thyristor and a method in which the rotational speed is controlled by an inverter.
A vacuum cleaner disclosed in the published application JP-A-60-242827 relates to the latter method. Namely, this cleaner uses a brushless motor which is driven by an inverter.
Although the motor which is driven by the inverter is disclosed in the foregoing published application, nothing is taught with respect to the technical concept of allowing the motor to be automatically operated in an optimum condition in accordance with the state of the cleaning surface or the choking state of the filter. In addition, means for implementing this technical concept is not disclosed or suggested.